I. Field
The present disclosure relates generally to electronics, and more specifically to semiconductor devices.
II. Background
Semiconductor devices such as transistors are commonly used in various active circuits such as power amplifiers. A power amplifier can provide amplification and high output power for a signal prior to transmission over the air. Hence, power amplifiers are used in virtually all wireless communication systems and in wireless devices as well as base stations.
A radio frequency (RF) power amplifier may impose conflicting requirements on transistors used to implement the power amplifier. For example, the high-speed RF power amplifier may require (i) a high breakdown voltage for the transistors in order to handle a large voltage swing and (ii) a high frequency of operation in order to handle an RF signal. For a transistor fabricated with a complementary metal oxide semiconductor (CMOS) integrated circuit (IC) process, the speed of the transistor may be increased by reducing the length of the gate. However, a shorter gate length also reduces the breakdown voltage of the transistor, which then limits the transistor's ability to handle a large voltage swing required for a power amplifier. Hence, it is difficult to obtain a high breakdown voltage and a high frequency of operation for CMOS transistors.
One conventional technique for achieving high speed and high output power for a power amplifier is to stack a number of transistors in a cascode configuration. Each transistor in the stack may then observe only a fraction of the output voltage swing. However, stacking transistors may result in degraded efficiency and a challenging circuit design in order to properly bias the transistors, avoid instability and oscillation, and simultaneously achieve high output power and efficiency. Another conventional technique for achieving high speed and high output power for a power amplifier is to construct transistors using a complicated device architecture. However, such a device architecture is often incompatible with standard CMOS process flow, which may require more mask and process steps to fabricate the transistors, may be difficult to integrate with conventional CMOS integrated circuits, and may result in higher cost. An RF power amplifier that is not difficult to fabricate and has low cost is thus highly desirable.